EP2156156B1 - Drive device comprising a drive shaft and a device for detecting torque - Google Patents

Description

Field of the invention

The invention is in the field of mechanical engineering and metrology. It can be used with various types of drive devices, such as bicycles, ergometers, pedelecs or other devices that can be driven by drive cranks. The invention relates both to a drive device and to a device which can be driven with at least one drive crank, in particular a bicycle, an ergometer or a pedelec.

In such devices, it may be useful to detect different sizes, such as the speed of bicycles and the distance traveled. For example, the instantaneous speed can give the driver an indication of whether it makes sense to choose a particular gear ratio or not.

In such a decision, however, it is useful to determine not only the speed but also the instantaneous torque applied to the force load of the parts of the bicycle and the force exerted by the driver, which is equivalent to the load on his skeleton, the musculature and the joints, to determine. These variables can also be decisive for the choice of a translation or for the decision to connect an auxiliary drive.

In addition, from the speed of the drive shaft in connection with a measured torque directly the power can be determined, which is introduced into the drive shaft.

From the state of the art, various possibilities for torque or torsion detection are known, some of which are also specialized in particular for use with drive cranks, in particular cranks for bicycles.

The DE 102005018286 A1 discloses an apparatus for determining a torque applied to a shaft, wherein a multipole magnet ring is provided in a first shaft portion of the shaft, and a stator holder having stator elements and fingers protruding in the axial direction is provided in a second shaft portion. Magnetic fluxes are more or less closed by a magnetic flux ring depending on the relative rotation of the shaft parts, so that the angle of rotation, which is a measure of the torsional forces, is measured.

From the DE 10225018293 A1 a torque sensor is known in which a magnet and a sensor unit is attached to two sections of the shaft in each case, wherein the sensor unit acts as a proximity switch and indicates a rotation of the shaft as a change in position of the magnet.

The DE 102005023182 A1 shows a torque detecting device with a torque transfer plate for transmitting torque between a motor output member and a torque converter drive member, wherein the transfer plate is slightly elastically deformable by targeted weakening due to a torque and wherein on deformable webs of the transfer plate strain gauges are provided for detecting the elastic deformation. About the function of the strain gauges nothing else is executed there.

The DE 102005041287 A1 shows a torque sensor with two partial waves, wherein each of the partial waves is connected to a so-called detection tube and the detection tubes are coaxial with each other. They are firmly connected to spaced apart locations on the partial waves and have frontally circumferential teeth, so that with more or less strong rotation of the shaft parts, the magnetic resistance between the detection tubes changes periodically depending on the agreement of the teeth. As a result, a rotation of the partial waves is detectable against each other. This is a measure of the acting torsional forces.

From the DE 10044701 C1 goes out a transmission device to the pedals of a bicycle, by means of which the pedal force is transmitted to the crank. An elastic element in the form of a spring is compressed by the power transmission and this force action is measured to determine the transmitted torque therefrom.

From the DE 69900898 T2 On the one hand, the connection of magnetostrictive elements for the torsion measurement is known, wherein the torsion is to be converted into an electrical voltage by a magnetic material.

The main object of the document, on the other hand, is a measurement of a torque by means of two jointly mounted disks, which are coupled by means of rotationally acting spring elements. The achieved angular offset allows the transmitted torque to be determined between both disks.

From the EP 1046893 B1 In principle, the use of the magnetostrictive effect for torque measurement and the attachment of a magnetostrictive ring element on a shaft for transmitting the torque and for utilizing the effect is known. However, there is described no construction directly related to the structure of a rolling bearing, in which a torque sensor is integrated. For measuring the magnetic field, a special sensor is described, by means of which the current is measured at high frequency in a saturation magnetization of a probe in different magnetization directions, whereby the magnetic field of the magnetostrictive element can be measured accurately.

US 5,816,599 A describes a drive device for a bicycle with a torque-detecting unit, outside of the bottom bracket cartridge, a coil unit is arranged, which cooperates with a provided outside of the bottom bracket cartridge coating. A disadvantage here is that the limited space of the shaft can be exploited only inadequate, especially in the axial direction, since the unit is arranged on a parked portion of the right crank.

It is the object of the invention to provide a structurally compact and positionally correct arrangement of the magnetic sensor to the shaft of the bicycle in order to effectively exploit the limited space just for bottom bracket shafts in bicycles space.

• dass der axiale Abschnitt der Antriebswelle eine permanente Vormagnetisierung aufweist,
• dass der axiale Abschnitt der Antriebswelle als Signalgeber für mindestens einen Magnetfeldsensor ausgebildet ist, und
• dass der Magnetfeldsensor in einer Tretlagerpatrone angeordnet ist.

This object is achieved by a drive device having a drive shaft rotatably mounted about an axis and having two drive cranks angularly rigidly connected thereto with respect to the axis in the circumferential direction and having an output element connected to the drive shaft for transmitting torque between the drive shaft and a load element a magnetostrictive sensor fixedly connected to the drive shaft and arranged axially between a drive crank and the driven element, wherein the magnetostrictive sensor comprises an axial section of the drive shaft as part, with the features essential to the invention:

• the axial section of the drive shaft has a permanent bias,
• that the axial portion of the drive shaft is designed as a signal generator for at least one magnetic field sensor, and
• that the magnetic field sensor is arranged in a bottom bracket cartridge.

The feature that the axial portion of the drive shaft has a permanent bias, offers the advantage, while maintaining the magnetostrictive measuring principle, a space-saving arrangement for the drive shaft to find.

The feature that the magnetic field sensor is accommodated in a bottom bracket cartridge has the advantage of providing a structurally compact and correct arrangement of the magnetic sensor to the shaft of the bicycle in order to effectively exploit the limited space just for bottom bracket shafts in bicycles space.

The fact that at least one magnetostrictive sensor is fixedly connected to the drive shaft divides any torsional load transmitted in the axial section of the shaft in which it is mounted.

Usually, the torque is introduced by means of a drive crank and transmitted to the output element by means of further coupled with this mechanical elements. Therefore, it makes sense to provide a magnetostrictive sensor axially between these two elements on the drive shaft.

In order to be able to detect the torque transmitted in total by the shaft at any time or even averaged, it is furthermore advantageous to provide at least one magnetostrictive sensor between each of the drive cranks and the output element.

In a bicycle, for example, it results from the physiological and physical basic conditions that a cyclist drives the two drive cranks / cranks simultaneously not the same time, but periodically changing and depending on the angular position of the respective drive crank.

It can be averaged over each of the drive cranks torque over time at least over half a turn of the drive shaft and the torques of both drive cranks can for example also be compared with each other to compensate for asymmetries in the driver.

The magnetostrictive sensors each have one or advantageously also two magnetic bodies made of a permanent magnetic, magnetostrictive material. This material is characterized in that in the unloaded state of the magnetization state is maintained, however, that at each deformation results in a change in the magnetic properties and thus a change in the stray field outside of the magnetostrictive body. Thus, by detecting the stray fields deformations and thus acting on the magnetostrictive body bending or torsional moments can be detected.

The corresponding magnetostrictive bodies may be formed so that the magnetic flux substantially within the body and a stray field ideally occurs outside only when a torsional or bending moment is applied.

The corresponding body can be glued, soldered or welded, for example, on the drive shaft, but they can also be glued or soldered in a recess, welded or pressed.

Since many types of steel meet the requirements of the magnetostrictive effect, the invention provides an axial portion of the drive shaft to be used by appropriate bias as a magnetostrictive body. This can be done, for example, that the drive shaft is penetrated by a high pulse-like current to achieve a high magnetization in the circumferential direction of the current path due to the Ampere's law.

The magnetized axial portion of the drive shaft thus fulfills the function of the above-described magnetostrictive body, namely, to be the signal generator of at least one magnetostrictive sensor.

For example, a plurality of magnetostrictive bodies may be formed concentrically as cylindrical bodies and magnetized in opposite directions in the circumferential direction, so that the stray magnetic fields largely compensate one another in the ground state. If such a magnetostrictive body consisting of two magnetostrictive bodies is twisted with the drive shaft, the result is, for example, an axial stray magnetic field component which can be detected by a magnetic field sensor.

It can also be advantageously provided that two magnetostrictive bodies of a sensor are arranged axially one behind the other. These can be magnetized in opposite directions, for example. In the axial edge regions of the magnetostrictive bodies so-called pinning regions can be provided, which fix the magnetic flux.

The above statements concerning one or more magnetostrictive bodies as signal transmitters for magnetic field sensors apply correspondingly if, according to the invention, the at least one axial section of the drive shaft itself has a magnetization and serves as a signal transmitter for one or more magnetic field sensors.

If an axial section of the drive shaft is designed as a signal transmitter for at least one magnetic field sensor, it is preferably provided that the axial section comprises a first, near-surface region and a second, surface-intensive region, wherein the near-surface region has a first magnetization and the surface-proximate region has a second magnetization in such a way that in the unloaded state of the drive shaft, when no external torque occurs, the first magnetization and the second magnetization cancel each other in magnitude and direction such that no magnetic field occurs outside the drive shaft. However, the first or second magnetization are matched to one another in their amount or by the dimension of the two regions such that the two magnetizations no longer cancel each other as soon as a mechanical stress, for example a torque acting on the drive shaft, occurs. In this case, outside the drive shaft occurs a magnetic field, which is detected by one or more magnetic field sensors.

Preferably, it is provided for the provided with a bias axial portion of the drive shaft, that provided in the longitudinal extent of the drive shaft to at least one side, particularly preferably on both sides of the axial portion of the drive shaft so-called 'pinning zones' In other words, areas in which the magnetic field drops significantly, so that in the longitudinal direction of the drive shaft, the magnetic field of the axial portion is substantially limited to this and stray fields in the longitudinal direction of the drive shaft are suppressed. The aforementioned 'pinning zones' can be similar to the biased axial portion of the drive shaft obtained by a current pulse of high intensity.

It goes without saying that magnetostrictive bodies or axial sections of the drive shaft provided with a bias according to the invention represent equivalent alternatives which may also be provided in combination with one another in order to form two or more signal generators for magnetostrictive sensors. The following statements apply, even if they should explicitly refer to magnetostrictive body, mutatis mutandis, in the event that an axial portion of the drive shaft has a bias, so in the event that the drive shaft itself is partially formed as a magnetostrictive body.

By thus generated in the load / torsion magnetic stray field components, which can be oriented differently and which are detected with different magnetic field sensors, interference fields can be compensated by computational consideration. For example, the geomagnetic field can be calculated out.

It can be used to achieve a higher accuracy and more than two, for example, up to eight, such magnetostrictive body with corresponding magnetic field sensors.

The magnetic field sensors may in principle have the known functionalities such as those of a forester probe or a Hall sensor.

It has proven to be particularly advantageous that a magnetic field sensor has at least one electrical coil with a ferromagnetic core, which is connected to an alternating current source for alternating magnetization of the core to saturation.

Such a changing determination of the flux density to be generated up to saturation makes it possible to determine the stray field intensity with particularly little effort and with particular accuracy. The measurement can also be carried out particularly quickly, since the changing magnetic field saturations can be easily achieved in the kilohertz range.

The magnetic field sensors deliver a magnetic field strength as a measurement result, which can be further processed to determine a bending or torque.

The magnetic field sensors are advantageously arranged stationary relative to the drive shaft, in a bicycle, for example in the bottom bracket cartridge or in the housing of the bottom bracket or attached to an outer ring of the corresponding rolling bearing of the drive shaft.

They are connected to an evaluation device, which assigns the magnetic field values corresponding torque values based on a stored in a memory device measurement table. It is also conceivable to use a simple calculation rule in order to determine torques from the measured magnetic field strengths.

The evaluation device can furthermore determine time-averaging average values, so that the average torque for each drive crank can be determined, for example, over half a revolution of the shaft and also in total for the drive shaft.

In addition, the torque can also be measured in the output train, so that any losses can be calculated.

If, in addition, the rotational speed of the drive shaft is measured or the speed of the bicycle, from which it is possible to calculate back to the rotational speed, the power can also be calculated taking into account the corresponding torques.

The evaluation device is advantageously connected to an analysis device in which threshold values for torques are stored in a memory device and compared by means of a comparison device with measured torque values.

The analysis device may in turn be connected to a control device, which may be connected to an auxiliary drive and / or a braking device of an ergometer or a switching device for a transmission.

In the analysis device, when a certain torque is exceeded on the drive shaft or on a drive crank, the decision can be made to limit the torque, for example by changing a gear ratio in the load element. For example, in the case of a bicycle, this can mean that a lower gear is switched if the torques are too high.

The corresponding switching thresholds can relate both to instantaneous values of the measured torque and to moving average values.

The decisions can also be made taking into account the speed or the power calculated from the speed and torque.

Likewise, the corresponding thresholds of the torque can be used to switch on an additional drive in a bicycle, for example in the form of an electric drive or in an ergometer to reduce or increase the pedaling resistance.

Changes the direction of the introduced torque, it can be concluded in particular during operation of a bicycle that braking is intended and from this information commands for the braking device can be derived so that, for example, an additional brake can be switched.

The measurement of torques in the drive shaft allows in the described applications a variety of control options and the arrangement of the corresponding magnetostrictive sensors in the drive shaft, it also means that the sensors are well protected by the encapsulation of the shaft against environmental influences. This will also prevent malfunction and damage the sensors are unlikely.

In the following the invention will be shown with reference to an embodiment in a drawing and described below.

Fig. 1

im Querschnitt eine Antriebswelle mit zwei Antriebskurbeln wie sie bei einem Fahrrad eingesetzt werden;

Fig. 2

eine dreidimensionale Ansicht der Anordnung aus Figur 1;

Fig. 3

die grundsätzliche Funktion der magnetostriktiven Sensoren;

Fig. 4

eine Anordnung mit zwei konzentrischen magnetostriktiven Körpem;

Fig. 5

schematisch die Änderung des Magnetfeldes durch den magnetostriktiven Effekt;

Fig. 6

eine Anordnung von zwei magnetostriktiven Körpern axial hintereinander;

Fig. 7

den Längsschnitt einer Antriebswelle mit zwei magnetostriktiven Sensoren;

Fig. 8a

eine erste Umsetzung der Ausgestaltung aus Figur 7;

Fig. 8b

zeigt den in Figur 8a eingekreisten Teil in vergrößertem Maßstab,

Fig. 9

eine zweite Ausgestaltung ähnlich der Konfiguration aus Flgur 7,

Fig. 10

schematisch eine Antriebswelle und einer nachgeschalteten Auswerteeinheit und Steuereinrichtung.

It shows

Fig. 1

in cross-section, a drive shaft with two drive cranks as used in a bicycle;

Fig. 2

a three-dimensional view of the arrangement FIG. 1 ;

Fig. 3

the basic function of magnetostrictive sensors;

Fig. 4

an arrangement with two concentric magnetostrictive bodies;

Fig. 5

schematically the change of the magnetic field by the magnetostrictive effect;

Fig. 6

an arrangement of two magnetostrictive bodies axially one behind the other;

Fig. 7

the longitudinal section of a drive shaft with two magnetostrictive sensors;

Fig. 8a

a first implementation of the embodiment FIG. 7 ;

Fig. 8b

shows the in FIG. 8a circled part on an enlarged scale,

Fig. 9

a second embodiment similar to the configuration of Flgur 7,

Fig. 10

schematically a drive shaft and a downstream evaluation and control device.

FIG. 1 shows a drive shaft 1 of a bicycle, which at each of its ends, each with a drive crank 2, 3, also called crank in this context, by means of a screw 4, 5 in the circumferential direction with respect to the axis 6 is fixedly connected rigidly. The shaft 1 is in two bearings 7, 8, which are designed as ball bearings, stored and housed protected in a bottom bracket 9.

The assembly consisting of the bearings 7, 8 and the shaft 1, can also be summarized in a so-called bottom bracket cartridge.

About a crank star 10, the drive shaft 1 is connected to a rim or a set of wheel rims 11, which represent the output element and drive a chain of the bicycle.

Axially in the middle of the shaft is applied to this a magnetostrictive body 12 in the form of a sleeve, for example, soldered or shrunk. This sleeve forms part of a magnetostrictive sensor whose second part is used by a magnetic field probe 13 for monitoring particular magnetic field components of the stray field of the magnetostrictive body 12. For example, the magnetostrictive body 12 may be permanently magnetized as a permanent magnet in the circumferential direction, so that the magnetic flux lines within the body rotate and are closed. It then occurs in the torque-free state virtually no stray field to the outside.

The magnetic field sensor 13 will therefore be able to detect any magnetic field components in this state.

If the shaft 1 and thus also the magnetostrictive body are subjected to a torsion, the magnetostriction effect results in additional magnetic field components which generate a changed stray field outside the magnetostrictive body. These can be detected by means of the magnetic field sensor 13 and are a measure of the deformation due to the torsion of the shaft first

By means of the magnetostrictive body 12, a torque can thus be detected, which is transmitted between the drive crank 3 and the output on the opposite side of the shaft 1.

In the FIG. 2 is shown in three-dimensional representation of a ring gear 11 and a set of sprockets, which forms part of a switchable transmission.

In addition, a crank star 10 can be seen, which is structurally related to the drive crank 2 and with its spokes corresponding spokes of the sprockets are bolted.

The crank star can be directly connected to the drive crank 2 or mounted rotatably on the shaft 1.

Furthermore, the housing 9 of the bottom bracket is shown, with a magnetic field sensor 13 having, for example, an electrical coil. For compensation purposes, it is also possible to provide a plurality of coils with corresponding cores, wherein the cores are magnetically reversed by impressing an alternating current, wherein a magnetic field strength to be detected is manifested by the fact that the current intensities to be generated in addition to saturation are different in the two directions of the magnetization. From this asymmetry, the detected magnetic field strength can be determined.

However, it is also conceivable to use commercial magnetic field probes such as Hall sensors or Förster probes.

FIG. 3 shows in the upper part of a three-dimensional view of a shaft 1 with a magnetostrictive body 12 which is pushed onto this as a sleeve and in the magnetic flux lines in the circumferential direction, indicated by the arrow 14, rotate closed.

At the circumference of the shaft, offset by 180 °, two magnetic field sensors 13, 15 are shown, which can detect stray magnetic field components.

In the lower part of the FIG. 3 the configuration with corresponding bearings and a bottom bracket cartridge is shown in a longitudinal section. The bearings are denoted by 7, 8, the respective torques are respectively introduced at the ends of the shaft 1 by means of drive cranks and not on a shown in detail, lying between the drive cranks, driven element transmitted.

However, the magnetostrictive sensor 12, 13, 15 can detect torsions only if the part of the shaft on which the magnetostrictive body 12 is arranged actually transmits torque, which is the case only when it is axially between the point at the torque is introduced and the output element is arranged.

In the FIG. 4 a possible arrangement with several magnetostrictive bodies is shown schematically, wherein axially seen on a short portion of the shaft 1, two concentric hollow cylindrical magnetic body 16, 17 are provided, which, as in the lower left part of the FIG. 4 is shown, are permanently magnetized in the opposite direction in the circumferential direction.

As a result of this configuration, any remaining stray fields cancel out in the unloaded state; in any case, there are no magnetic field components directed in the axial direction of the shaft 1.

In the lower right part of the FIG. 4 1, there is shown an unrolling of the bodies 16, 17, from which it can be seen that the magnetic flux has no component in the axial direction 6 of the shaft.

The FIG. 5 shows in the left part of the illustration, a hollow cylindrical magnetostrictive element 16 in the unloaded state and about the unrolling with the symbolization of the magnetic flux lines exclusively in the circumferential direction.

In the right part of the figure, the twisted, loaded with a torque state of the magnetostrictive body is shown, wherein defined pieces of material which extend axially in the unloaded state, in the loaded state form helical cutouts from the hollow cylindrical body 16.

This results, as shown in the right upper part of the FIG. 5 shows additional axial components of the magnetic flux, which lead to the formation of axial components of the stray magnetic field.

These can be easily detected by magnetic field sensors.

The FIG. 6 shows a variant in which in the left part of the figure, a sleeve 16 is inserted into the shaft or formed as part of the shaft, provided that it consists of a matching magnetostrictive material.

Axially on both sides of the magnetostrictive body 16 so-called pinning regions 18, 19 are provided, which stabilize the magnetic field.

As dashed lines partially axially directed stray fields are shown, which occur at a torsional load and can be detected.

In the right part of the figure, two sleeves 16, 20 arranged axially one behind the other on the shaft 1, wherein the magnetization of the sleeves 16, 20 each in the circumferential direction of the shaft 1, but in opposite directions to each other.

On both sides of the magnetostrictive body 16, 20 pinning regions 21, 22 are provided for stabilizing the magnetic field.

As a result of this arrangement, the anisotropy effects in the magnetostriction result in axially directed stray magnetic field components in respectively opposite, axial directions. These can be detected by means of two magnetic field sensors 23, 24, whereby interference fields can be calculated out or compensated. It can thus be achieved with a combination of more magnetically strict body higher measurement accuracy.

In the FIG. 7 a configuration is shown in which the drive shaft 1 is mounted in the bearings 7, 8 and axially in the region outside the interspace of the bearings 7, 8, two magnetostrictive bodies 25, 26 are arranged. Each of the magnetostrictive bodies is associated with a magnetic field sensor 27, 28 for measuring the stray field components and thus for detecting the applied torque.

If the output element of the drive shaft lies between the magnetostrictive bodies 25, 26, then the torque introduced from both ends of the shaft can be determined individually between the drive crank and the output element. This can be determined in a simple manner, the sum of the torques acting on the drive shaft, which is relevant for the total load and the applied power.

The FIG. 8a shows a longitudinal section through a bottom bracket assembly with a shaft 1, an encapsulation 9 of the bottom bracket, ball bearings 7, 8 and drive cranks 2, 3rd

In this construction, the drive torque is introduced by the drive cranks 2, 3 in the shaft 1 and the output element is connected as a disc or pedal crank 29 directly to the shaft 1 rotatably. On the other hand, the sprockets 11 are connected to the crank star 29.

The torque is thus transmitted on one side of the drive crank 2 axially via the drive shaft 1 to the crank star 29, so that a magnetostrictive body 25 can be arranged axially between these elements. This is integrated into the shaft 1 and surrounded by a sensor ring 27 with one or more magnetic field sensors. By means of this sensor can thus measure the transmitted from the drive crank 2 to the output element 29 torque.

The torque transmitted between the drive crank 3 and the driven element 29 can easily be detected with a magnetostrictive body 30 axially in front of the bearing 7, but theoretically also everywhere between the bearing 7 and the bearing 8. In the figure, the second magnetostrictive body 30 is shown in the vicinity of the drive crank 3 and also surrounded by a sensor ring 31 with one or more magnetic field sensors.

In the FIG. 9 in the left and in the right half of the illustration, two variants are compared with each other, wherein in the right variant, the magnetostrictive body on both sides directly axially next to the output element 29 and each surrounded by sensor rings 27, 31. The magnetostrictive bodies are designated 25, 30.

In comparison, the magnetostrictive body are arranged on the one hand between the output element 29 and the drive crank 2 in the left part of the figure, wherein the magnetostrictive body is again denoted by 25, the sensor ring 27. On the other hand, a second magnetostrictive sensor is arranged in the immediate vicinity of the drive crank 3, designated there by 30 and also surrounded by a sensor ring 31.

To determine the two introduced by the drive cranks 2, 3 torques in the drive shaft 1, both variants are equivalent.

FIG. 10 schematically shows a drive shaft 1 with two magnetostrictive bodies 25, 30 and corresponding magnetic field sensors 27, 31 and drive cranks 2, 3 and an output member 29th

In addition, a speed sensor 32 is shown which cooperates with an element 33 mounted on the shaft.

The magnetic field sensors 27, 31 are connected to an evaluation unit 34. In this memory device 35 is provided, which contains a value table, by means of which the measured magnetic field strengths individually torque values can be assigned. Thus, the torque values are currently detectable axially on both sides of the output member 29 and can also be averaged over time. They can be added together to calculate or subtract a total torque to detect any asymmetries between the torque applied from left to right.

By means of the speed sensor 32, in cooperation with a time base 36, a speed can be determined which can be used together with the detected torque values for a performance determination.

The corresponding evaluated data are forwarded to an analysis device 37, in which threshold values for specific control options are stored. These are stored in a second memory device 38 and compared with the measured values by means of a comparison device 39.

In this case, power values can be compared, instantaneous torque values or time-averaged torque values.

As reaction options is for a control device 42, the operation of a switching device 40 for changing a transmission ratio available or the control of an auxiliary drive 41, in a bicycle, for example, an electric drive.

Thus, by means of the invention, in a simple manner and without fundamentally interfering with the construction of a machine, the torque at the drive shaft can be measured at one or more points, and an assistance function can be activated by means of a control device that, for example, in the application of bicycles, the driver a higher ride comfort is provided.

The drive device described above may further comprise a transmission device for the detected measured values. The transmission device transmits the recorded measured values to a receiver arranged outside the machine, for example by radio or by IR signal.

LIST OF REFERENCE NUMBERS

1

drive shaft

2, 3

drive crank

4, 5

screw

6

axis

7.8

camp

9

bottom bracket

10

crank star

11

rims

12, 25, 26

magnetostrictive bodies

13, 15, 23, 24, 27, 28

magnetic field sensor

16, 17, 20

Hollow cylindrical magnetic body, sleeve

18, 19, 21, 22

Pinningregionen

29

Tretkurbelstern

30

magnetostrictive body

31

sensor ring

32

Speed sensor

33

evaluation

35

memory device

36

time basis

37

analyzer

38

memory device

39

comparator

40

switching device

41

auxiliary drive

Claims (19)

1. Drive device comprising a drive shaft (1) mounted so as to rotate about an axis (6), and comprising two driving cranks (2, 3) connected to said shaft in the circumferential direction with respect to the axis in an angularly rigid manner, and comprising an output element (29) which is connected to the drive shaft (1) and has the purpose of transmitting torque between the drive shaft (1) and a load element, comprising a magnetostrictive sensor (12, 13, 25, 27, 30, 31) which is permanently connected to the drive shaft (1) and is arranged axially between a driving crank (2, 3) and the output element (29),
   wherein the magnetostrictive sensor (12, 13, 25, 27, 30, 31) comprises an axial section of the drive shaft as a part,
   characterized
   in that the axial section of the drive shaft (1) is permanently pre-magnetized,
   in that the axial section of the drive shaft (1) is embodied as a signal generator for at least one magnetic field sensor, and
   in that the magnetic field sensor is arranged in a bottom bracket cartridge.
2. Drive device according to Claim 1,
   characterized
   in that in each case a magnetostrictive sensor (12, 13, 25, 27, 30, 31) is arranged axially between each of the driving cranks (2, 3) and the output element (29).
3. Drive device according to Claim 1 or 2,
   characterized
   in that the magnetostrictive sensor (12, 13, 25, 27, 30, 31) has at least two magnetized sections of the drive shaft (1) which are permanently pre-magnetized.
4. Drive device according to Claim 3,
   characterized
   in that the two magnetized sections are magnetized in opposite directions in the unloaded state.
5. Drive device according to Claim 3 or 4,
   characterized
   in that the two magnetized sections of a magnetostrictive sensor (16, 20, 23, 24) are arranged lying axially one behind the other.
6. Drive device according to Claim 5,
   characterized
   in that the magnetic field components which are generated by the two magnetized sections by means of torsion have different directions.
7. Drive device according to one of Claims 1 to 6,
   characterized
   in that the at least one axial section of the drive shaft (1) comprises a first region, near to the surface, with a first magnetization and a second region, remote from the surface, with a second magnetization, wherein the first magnetization and the second magnetization are added in a mechanically unloaded, in particular torque-free, state of the drive shaft (1) to form an essentially diminishing magnetic field outside the drive shaft (1).
8. Drive device according to one of Claims 1 to 7,
   characterized
   in that a pinning zone is arranged on at least one side of the axial section, provided with the magnetization, of the drive shaft (1), said pinning zone limiting the magnetic field, which can be measured outside the drive shaft (1), of the axial section essentially to the region of the axial section.
9. Drive device according to one of Claims 1 to 8,
   characterized
   in that a magnetic field sensor (13, 15, 27, 31) for measuring the magnetic leakage field is assigned to each magnetostrictive sensor (12, 13, 25, 27, 30, 31).
10. Drive device according to Claim 9,
    characterized
    in that a magnetic field sensor (13, 15, 27, 31) is assigned to each axial section, provided with magnetization, of the drive shaft.
11. Drive device according to Claim 9 or 10,
    characterized
    in that a magnetic field sensor (13, 15, 27, 31) has at least one electrical coil with a ferromagnetic core, said coil being connected to an alternating current source for the purpose of alternating magnetization of the core up to saturation.
12. Drive device according to Claim 9, 10 or 11,
    characterized
    in that the magnetic field sensor or sensors (13, 15, 27, 31) are arranged in a positionally fixed fashion with respect to the drive shaft (1).
13. Drive device according to one of Claims 1 to 12,
    characterized by
    an evaluation device (34) which is connected to the magnetic field sensors (27, 31) and assigns torque values to the measured magnetic field values.
14. Drive device according to Claim 13,
    characterized by
    an analysis device (37) in which threshold values for torques are stored in a memory device (38) and are compared with measured torque values by means of a comparison device (39).
15. Drive device according to Claim 14,
    characterized by
    a control device (42) which is connected to the analysis device (37) on the one hand, and to an additional drive (41) and/or a shifting device (40) for a transmission, on the other.
16. Drive device according to one of Claims 1 to 15, further comprising a transmission device which transmits the sensed measured values to a receiver, in particular by radio or IR signal.
17. Drive device according to one of Claims 1 to 16, characterized in that in order to bring about the pre-magnetization of the magnetized axial section of the drive shaft (1), a high, pulse-like current was passed through the drive shaft (1) in order to achieve a high level of magnetization in the circumferential direction of the current path.
18. Drive device according to one Claims 1 to 17, characterized in that a rotational speed sensor (32) is provided which interacts with an element (33) attached to the shaft.
19. Device which can be driven by means of at least one driving crank, in particular a cycle, ergometer or pedelec, characterized by a drive device according to one of Claims 1 to 18.

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